Patent document 1 describes a known technique that makes room temperature approach a set temperature.
In the technique, the evaporation temperature is set at a predetermined value (hereafter, referred to as the “set evaporation temperature”) so that the room temperature approaches the set temperature. Then, the displacement of a compressor is controlled so that the evaporation temperature is maintained at the set evaporation temperature. Consequently, the room temperature approaches the set temperature.
In the case of this technique, the evaporation pressure is maintained at a set evaporation pressure so that the evaporation temperature is maintained at the set evaporation temperature (e.g., 5° C.) during a cooling operation. Additionally, to maintain the evaporation pressure at the set evaporation pressure, the suction pressure of the compressor, which is correlated with the evaporation pressure, is used as a control parameter. The operating frequency of a motor of the compressor is controlled so that the suction pressure approaches a target suction pressure, which corresponds to the set evaporation temperature.
During a cooling operation, a pressure loss occurs in a low pressure refrigerant circuit, which extends from the indoor heat exchanger to the compressor. The pressure loss differs between air conditioners. The value of the pressure loss varies depending on the installation condition of each air conditioner. Such a variation is mainly caused by the length of a low pressure refrigerant connection pipe extending from the indoor heat exchanger to the compressor.
Under the assumption that the evaporation pressure is equal to the suction pressure, the displacement of the compressor may be controlled so that the suction pressure approaches the target suction pressure, which corresponds to the set evaporation temperature. In such a case, since the pressure loss is not considered, the evaporation pressure may fail to approach the set evaporation pressure.
In this regard, patent document 2 describes a technique in which the pressure loss is considered when the displacement of a compressor is controlled so that the refrigerant suction pressure approaches a target suction pressure. More specifically, during a test-run performed when installing an air conditioner, a pressure loss estimation value, which is a correction amount for the suction pressure, is obtained. Then, the target suction pressure is set taking into consideration the pressure loss estimation value. In this manner, the target suction pressure is changed to a value that takes the pressure loss estimation value into consideration. Thus, the evaporation pressure can quickly approach the set evaporation pressure.